Conventionally, there is a known method as disclosed in Japanese Patent Application Laid-open No. 6-331505 in which a bench testing machine having rollers for front wheels and rollers for rear wheels is used and the front and rear wheels of a vehicle are rotated on the corresponding rollers to measure a lateral displacement amount of the vehicle. In this method, the bench testing machine is provided with adjusting wheels for coming in contact with the respective wheels of the vehicle from a lateral direction and load cells each for detecting a force of each wheel pressing back each wheel in a lateral direction. An input load of the load cell when the wheel is rotated on the roller is converted into the lateral displacement amount based on data showing correlation between a load cell input load and the amount of lateral displacement and collected by measuring the input load of a measuring apparatus and by measuring the lateral displacement amount in an actual traveling test on a common vehicle in advance and an evaluation of lateral displacement on a pass/fail basis is conducted based on whether the lateral displacement amount is equal to or less than a reference value.
Conventionally, there is also a known method as disclosed in Japanese Patent Application Laid-open No. 8-43263 in which a bench testing machine is provided with a swinging frame for moving back and forth in a lateral direction toward side sills of a vehicle and for swinging about a vertical axis, the swinging frame is mounted with a pair of measuring rollers in contact with front and rear two positions of the side sills of the vehicle, and a lateral movement amount and a swinging angle of the swinging frame are detected in a rotating state of wheels and are respectively compared with each reference value to thereby conduct an evaluation of lateral displacement on a pass/fail basis.
In the former prior art, however, the data showing the correlation between the load cell input load and the lateral displacement amount need be obtained for each vehicle type, which require much time and labor. Moreover, because the data are obtained by bringing the adjusting wheels into contact with side faces of a tire of the respective wheels, data values are affected by projections and depressions on the side faces, true data cannot be obtained, and reliability decreases. Furthermore, contact marks may be left on the tires by the adjusting wheels which have come in contact with the tires.
In the latter prior art, translational motion of the vehicle in the lateral direction is detected as the lateral movement amount of the swinging frame and yawing motion of the vehicle is detected as the swinging angle of the swinging frame. Even if the vehicle is displaced laterally, much time is required for the vehicle to move laterally or yaw to such a degree as to be detected and it is difficult to measure in a short time. Moreover, because the measuring rollers are brought into contact with the side sills, the side sills may be damaged.
With the above points in view, it is an object of the present invention to provide a method of measuring the lateral displacement amount of the vehicle accurately in a short time without damaging a vehicle body and tires by using a bench testing machine.